International pressure

US officials called on countries to cut all imports of Iranian oil when it re-imposes sanctions on Tehran.

It called on allies in Europe, Asia and the Middle East to adhere to the sanctions with the aim of pressuring Iran into negotiating a new agreement.

Hook said he planned to meet with European allies Britain, France and Germany at the end of the week to discuss Iran. He also said he and senior Treasury Department officials would visit Gulf states "in the coming days."

Hook told reporters that the goal of the United States was to get as many countries as possible down to zero Iranian oil imports.

"Our goal is to increase pressure on the Iranian regime by reducing to zero its revenue on crude oil sales," Hook said.

"We are working to minimize disruptions to the global market but we are confident there is sufficient global spare oil capacity."

Hook said more than 50 international firms have already announced their intention to leave the Iranian market, especially in the energy and financial sectors.

"We have been clear with countries and companies around the world that we are bringing severe economic pressure on Iran until the regime changes its destabilizing policies," Hook said.

Saudi Arabia's King Salman promised Trump at the weekend that he would raise oil production if needed and that the country has 2 million barrels per day of spare capacity to boost output, the White House said.

In a tweet on Saturday, Trump said the extra Saudi oil would help offset a decline in supply from Iran.

He was not specific on whether the additional two million barrels was a per-day figure - but worldwide daily demand is nearing 100 million bpd.